1. Field of the Invention
The present invention relates to a switch having a housing which receives a temperature-dependent switching mechanism and has a lower part on whose inner base a first countercontact for the switching mechanism is arranged, as well as a cover part, closing off the lower part, on whose inner side a second countercontact for the switching mechanism is provided, the switching mechanism creating, as a function of its temperature, an electrically conductive connection between the two counter-contacts, to which contact can be made from outside.
2. Related Prior Art
A switch of this kind is known from DE 37 10 672 A1.
In the case of the known switch, the housing has a lower part made of electrically conductive material as well as a cover part, closing off the lower part, that is made of insulating material. The switching mechanism, which comprises a spring disk that carries a movable contact element, is arranged in this housing. The spring disk operates against a bimetallic snap disk that is slipped over the movable contact element. Below the switching temperature the spring disk, which is braced against the base of the lower part, presses the movable contact element against a countercontact that is provided on the inside of the cover and extends outward, in the manner of a rivet, through the cover. The base of the lower part serves as further countercontact for the switching mechanism.
Since the spring disk itself is made of electrically conductive material, below the response temperature of the switching mechanism it provides a low-resistance electrically conductive connection between the countercontact on the cover part and the countercontact on the lower part, contact being made from outside to the lower part. If the temperature of the switching mechanism is then increased, the bimetallic snap disk suddenly snaps over and pushes the movable contact element, against the force of the spring disk, away from the countercontact on the cover, so that the electrical connection is broken.
Switches of this kind are commonly used for temperature monitoring of electrical devices. As long as the temperature of the electrical device does not exceed a predetermined response temperature, the switch, which for this purpose is connected in series with the load being protected, remains closed. If the temperature of the load then increases excessively, the bimetallic snap disk snaps over and thus interrupts the flow of current to the load.
It is a disadvantage of the known switch that it is relatively complex to produce. This is due principally to the fact that after production of the cover part, the countercontact must then be fastened onto the cover part; at the same time, an electrically conductive connection out through the wall of the cover part must be provided. This is done in the manner of a rivet that transitions, outside the cover, into a head to which conductors, crimp terminals, etc. can be soldered. This assembly of the countercontact to the cover is generally performed manually, and is thus very cost-intensive.
A further switch, in whose housing a temperature-dependent switching mechanism as described above is also arranged, is known from DE 21 21 802 A. In this switch the cover part and lower part are both cup-shaped, and are made of electrically conductive material. One-piece crimp terminals are shaped onto both the upper part and the lower part, the crimp terminal of the lower part extending outward through a corresponding cutout in the wall of the upper part. An insulating film is arranged between the upper part and the lower part in order to insulate the two housing parts electrically from one another.
The temperature-dependent switching mechanism thus makes contact on the one hand with the lower part via the spring disk, and on the other hand with the cover part via the movable contact element, so that an electrically conductive connection between the two crimp terminals exists as long as the temperature of the switching mechanism is below the response threshold. If the temperature of the switching mechanism rises, this electrical connection is broken in the manner described above.
Final assembly of this switch is also very complex due to the insulating film that must be introduced, and therefore can only be accomplished manually. This manual final assembly is not only wage-intensive, but also leads to assembly errors and thus to a higher reject rate.
A further disadvantage of both switches described so far is the fact that for certain applications they must be additionally insulated externally, since current flow occurs via the electrically conductive lower housing part.
A further temperature-dependent switch which has a lower housing part made of insulating material and a cover, made of metal, that rests on a shoulder of the lower part and is held by a rim of the lower part, is known from U.S. Pat. No. 4,490,704. The temperature-dependent switching mechanism comprises a bimetallic spring, clamped at one end, that at its free end holds a movable contact that is in contact, below the response temperature of the switching mechanism, with a fixed countercontact that is arranged on the inside of the cover.
At its other end, the bimetallic spring is firmly clamped and connected to a resistor that extends on the base of the lower part. A through hole, into which a knob-like connector element is inserted from below, is provided in the base. This connector element is soldered to the resistor at its head projecting into the interior of the switch. The knob-like head continues into a bracket that extends laterally under the wall of the lower part and continues, alongside the lower part, into a connector lug.
This document therefore describes a temperature-dependent switching mechanism completely different from the two documents cited above; because of the bimetallic spring clamped at one end, the demands in terms of insulation of the switching mechanism are less stringent in the various switching states.
Because of the knob-shaped connector element, making contact with the clamped-in end of the bimetallic spring is very laborious: not only are parts of complex shape required, but because the knob-like head is soldered to the resistor in the interior of the lower part, assembly is very laborious. A further disadvantage of this switch is that it is uninsulated at both the top and the bottom, so that particular precautionary measures are required when installing it on the device to be protected.